It is a game, but it already has a feature which many games do not have, which is that the players don't really know the rules, but have to figure them out from experience. They don't publish the rates at which things train, as it is, for instance, but leave us to figure them out. Playing this game assumes a certain acceptance that things aren't going to work in a predictable fashion, so I think the developers can assume their players are already pre-selected to have a tolerance for that sort of thing.
If this game didn't resemble basketball at all, not very many people would be playing it either. All things being equal, approaching reality is a good thing. Of course there's balance in terms of making it a good game as well.
It's not the change I would have made; I would rather have people not in the positions being trained get some training, which would really mess with people's attempts to stop players from developing to keep them under the salary cap. I think managing salary cap by withholding training is kind of bogus anyway, it's pretty anti-thematic. However, it's required by another odd mechanic, which is that everyone has a one year contract. If you had a guy on a 5 year contract, you'd train him to the max and not worry about it.
In the end, it's just 10%. It's not a huge deal, it's a tweak. There are things much more annoying than cross-training in this game, and yet it's still quite fun. I think on the whole I actually like it, but it's not big enough for me to even feel strongly that way.